1. Field of the Invention
This invention relates to a non-coated gravure printing paper that provides excellent gravure printability through the achievement of better adhesion between the photogravure cylinder and the paper, thereby reducing the generation of speckles.
2. Description of the Related Art
Gravure printing is a type of intaglio printing and therefore it requires a high degree of adhesion between the paper and the photogravure cylinder during printing. Poor adhesion between the paper and photogravure cylinder results in poor transfer of the ink, the likely result of which is the generation of so-called “speckles,” or small white spots, particularly in half-tone areas. The speckles invariably reduce the quality of the printed result. Good adhesion is achieved through the high smoothness and cushioning property of the paper. If the paper is smooth, it adheres more closely to the photogravure cylinder. A higher cushioning property allows the paper to deform under pressure during printing and thereby achieve better adhesion to the photogravure cylinder. These effects reduce the occurrence of speckles and thus improve printing quality.
Certain types of pulp and filler—two key ingredients in the production of paper—are selected to achieve higher smoothness and cushioning in a gravure printing paper. As for pulp, the content of mechanical pulp (such as groundwood pulp and refiner groundwood pulp) is maximized to increase the degree of cushioning. If chemical pulp materials must be used, ones having softer fibers are selected. To achieve a smoother surface, normally a gravure paper contains approximately 30% filler. This is more than the level found in offset printing papers, for example, where the filler content is generally 20% or less. Various other agents are added to the pulp and filler mixture, which is then made into paper. The obtained paper then undergoes a process of super-calendering to ensure high smoothness. While a filler consisting of fine, plate-shaped grains improves smoothness, the use of a filler containing grains that are too small in size increases the generation of speckles, although the smoothness does improve. Therefore, the filler content must be limited. Amid increasing environmental awareness throughout the public and industry of late, the use of recycled, ink-removed pulp is now favored over virgin pulp in both mechanical and chemical pulp applications. With chemical pulp it has become difficult to selectively source high-grade wood material from which flexible fibers can be obtained, or to procure chemical pulp made from such high-grade wood material. As a result it has become increasingly important to design quality gravure printing papers that generate less speckling, in addition to seeking the optimal blend of filler and pulp.